The overall objective of this controlled, prospective, multidisciplinary study is to identify and investigate risk factors associated with the development of asthma in individuals who develop allergy to laboratory animals in an occupational setting. Specific objectives relate to the following questions: 1) Is the existence of allergy (symptoms and/or sensitivity) prior to exposure a risk factor for asthma? 2) Are family history and demographic factors risk factors for asthma? 3) Is the pre-existence of airway hyperreactivity a risk factor and is there an association between changes in airway hyperreactivity and asthma? 4) What are the quantitative and qualitative characteristics of suspended airborne particulate matter, including animal allergens, at selected sites and 5) Is the level of exposure of laboratory workers to specific, respirable animal allergens a risk factor? The study will be conducted within the population of research laboratory workers at the Johns Hopkins Medical Institutions and University. Study subjects will be enlisted over a 3 1/2 year period when they first come here to work with laboratory animals. They will be evaluated semi-annually by interview, allergy skin tests, in vitro assays for total serum IgE and IgE antibodies specific for allergens of the principal laboratory animals, and pulmonary function tests including bronchial challenge with methacholine. Environmental samples will be collected at selected sites within the JHMI and in the personal breathing zones of a sample of laboratory workers. Both respirable and nonrespirable fractions of suspended particulate matter trapped in the air sampling devices will be analyzed qualitatively and quantitatively, including assays for specific animal allergens. We will estimate an Index of Exposure from personal work histories and measure actual exposure using air sampling devices. The results of these studies are expected to contribute significantly to our understanding of the pathogenesis of asthma in general and the role of airway hyperreactivity in this disorder. As occupational asthma is an increasingly important problem, improved understanding of the risk factors and mechanisms will hopefully lead to the development of promising new approaches to successful disease prevention.